At a Glance

Disease Syndrome

Myocarditis and pericarditis, nonischemic inflammatory conditions of the myocardium and pericardium, respectively, are frequently coexistent disorders with disparate manifestations and causes, both infectious and noninfectious. Acute signs and symptoms tend to be nonspecific and include fever, palpitations, malaise, myalgias, and arthralgias, potentially accompanied by some combination of tachycardia, arrhythmias, dyspnea, chest pain, productive cough, and heart failure. It is appropriate to entertain a diagnosis of acute infectious myocarditis and/or pericarditis in a younger individual presenting with chest pain, arrhythmia, or heart failure of unknown origin, especially in the setting of a recent or concurrent upper respiratory infection or other nonspecific febrile illness.

Classic presentations notwithstanding, myocarditis and pericarditis are not necessarily restricted to the young and may occur absent a clear history of accompanying infection. Frequent subclinical occurrence and nonspecific disease presentations probably lead to under-diagnosis. Furthermore, myopericarditis may be clinically indistinguishable from acute coronary ischemic events.

Causative Agents

The etiologic spectra of myocarditis and pericarditis overlap almost completely and mirror the range of human microbial pathogens capable of systemic infection. However, viruses are the predominant etiology in North America and Western Europe. Application of increasingly sensitive molecular techniques has substantially expanded and diversified the scope of viruses associated with myocarditis and pericarditis. Among approximately 20 implicated viral etiologies, those primarily associated with myocarditis in children and young adults are adenovirus, coxsackievirus type B (CBV), human herpes virus 6B (HHV-6), and parvovirus B19 (B19).

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

General Methods of Laboratory Diagnosis

Principal laboratory approaches to the diagnosis of viral myocarditis and pericarditis are the invasive techniques of endomyocardial biopsy (EMB), pericardial biopsy, and pericardiocentesis; noninvasive testing of noncardiac specimen types (e.g., oropharyngeal secretions, urine, and stool); and virus-specific serologic assays. The diagnostic gold standard of viral myocarditis is met by demonstration of inflammatory myocardial damage and viral components in cardiac tissue.

Culture and nucleic acid amplification testing (NAAT; often polymerase chain reaction (PCR) or nucleic acid sequence-based amplification) are the primary methods of virus detection. Serology can provide chronologic insight into the patient's immunologic experience with the suspected cause and, thereby, substantiate or challenge an etiologic diagnosis suggested by other clinical and laboratory abnormalities. Detection of virus in a peripheral specimen with concurrent serologic confirmation of recent infection constitutes the highest level of circumstantial evidence among compatible signs and symptoms. Virologic or serologic markers of infection, when taken alone, offer weaker (and minimally acceptable) evidence for a specific viral etiology.

Tests for Major Causes of Viral Myocarditis

The following tests are suitable for evaluating the most commonly recognized causes of viral myocarditis in the absence of a definitive diagnostic specimen (i.e., virus- positive EMB, pericardial tissue, or pericardial fluid).

Parvovirus B19:

HHV-6:

NAAT of whole blood, serum, or plasma

Serology performed on acute and convalescent specimens

Tests for Less Common Causes of Viral Myocarditis

The following tests are useful for evaluating unusual causes of viral myocarditis that may be considered in settings of compatible clinical or laboratory findings, immune compromise, or unsuccessful attempts to identify more commonly identified myocarditic viruses.

Influenza:

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Agent-Specific Factors Affecting Interpretation of Laboratory Results

Enteroviruses

The anatomic location of peripherally detected enteroviruses strongly influences an interpretation of pathologic significance. Cardiac involvement is supported by viremia and viruria, which are indicative of active infection with systemic viral spread. Virus detection in throat, respiratory, and gastrointestinal (GI) specimens must be appreciated in terms of the well-known potential for prolonged (up to months) asymptomatic shedding from the nasopharynx and GI tract and, thus, possible coincidental association with cardiac abnormalities.

Some CAV serotypes are very difficult to isolate in cell culture, and NAAT is the only consistent means of detecting these viruses in clinical specimens.

Adenovirus

Adenovirus viremia is a specific finding of pathologic viral replication, optimally diagnosed using NAAT due to low sensitivity of culture.

Respiratory disease in otherwise healthy pediatric subjects may be followed by asymptomatic viral shedding from the respiratory and GI tracts for several weeks or months, respectively. Specimens collected nearest the time of acute illness contribute greatest diagnostic value.

Primary infections fail to elicit virus-specific IgM in more than 50% of cases, and seroconversion may be delayed or absent in children and immunocompromised hosts, respectively. Demonstration of virus-specific IgM in the absence of IgG, seroconversion from negative to positive IgG, or greater than or equal to four-fold elevation in IgG titer confirms recent or acute adenovirus infection. The presence of virus-specific IgG in the absence of IgM indicates past infection at an undetermined time. Dual IgM/IgG positivity for adenovirus is compatible with recent/acute infection, yet fails to perfectly predict infection history, since IgM may reappear during virus reactivation.

Parvovirus B19

NAAT for circulating virus is essential in the evaluation of immunocompromised hosts.

IgM antibodies sometimes persist for more than 6 months. Therefore, detection of low-level IgM may not reflect recent or acute infection.

Prolonged tissue persistence of B19 in healthy individuals and frequent codetection of B19 with other known viral causes of myocarditis obscure the role of B19 in disease.

HHV-6

Detection of viremia by NAAT methods usually corresponds to active viral replication. High or increasing viral loads determined using quantitative assays may be helpful for distinguishing active from latent infection.

Persistently very high viral loads (>103.5 and >106 genome copies/ml of serum and whole blood, respectively) occur in approximately 1% of individuals because of germline integration of HHV-6 DNA. Chromosomally integrated viral DNA is indicated by positive NAAT using multiple different types of specimens, such as blood, hair follicles, and buccal swabs.

One should test for HHV-6 IgG in conjunction with IgM when evaluating possible acute or recent infection since IgM prevalence in the adult population approximates 5% due to viral reactivation from latency or reinfection.

Frequent association of HHV-6 with other known viral causes of myocarditis complicates accurate appraisal of HHV-6 contribution to disease.

CMV

Qualitative NAAT methods, although generally more sensitive than quantitative assays for detection of CMV in blood, may not discriminate active CMV disease from asymptomatic replication and latent infection in immunocompromised hosts and healthy individuals, respectively.

The best indirect evidence of CMV-related myocarditis or pericarditis beyond the perinatal period is established by high or rising levels of viremia in concert with compatible signs and symptoms. In cases of suspected congenital infection, viruria is a clinically significant finding reflective of systemic viral replication; testing should be performed within 1 week of birth to exclude post-partum infection as an explanation for viruria.

Documentation of a greater than or equal to four-fold elevation in CMV-specific IgG titer or seroconversion from negative to positive virus-specific IgG confirms recent or acute CMV infection. Baseline serum should be collected early during acute disease presentation and tested concurrently with convalescent serum acquired 2-4 weeks later.

Except in the newborn, CMV IgM does not necessarily correspond to recent or acute infection. Virus-specific IgM may reappear during reactivation of latent CMV and persist 6-9 months following primary infection. Additionally, false-positive IgM assays are possible due to heterotypic antibodies elicited by EBV infection. It is advisable to perform EBV-specific serologic testing when interpreting the significance of CMV IgM positivity. IgM production may be delayed or absent in newborns and immunocompromised patients.

EBV

Disease attributable to active EBV infection correlates most closely with viremia. Detection of circulating EBV (especially rising virus titers) by quantitative NAAT provides the strongest possible indirect support for a diagnosis of EBV-related myocarditis or pericarditis when accompanied by compatible clinical signs and symptoms.

The defining hematologic abnormality of acute EBV infection, occurring in approximately 70% of cases, is an exuberant absolute lymphocytosis and monocytosis containing a large fraction of atypical lymphocytes.

A positive heterophile antibody test provides sufficient support for diagnosis of primary EBV infection in the setting of typical infectious mononucleosis (IM)-like illness. However, EBV-specific serologic assays are warranted in the laboratory investigation of complicated or unusual EBV manifestations, such as myocarditis and/or pericarditis, to clinically interpret the heterophile antibody status and clarify disease etiology.

Appearance of heterophile antibodies may be delayed 3-4 weeks following onset of acute EBV illness. Heterophile antibody-negative infection, 10-15% on average, occurs disproportionately in children (≥50% of children <4 years of age). Depending on the particular test system employed, assayable heterophile antibodies may persist for several months following infection. CMV infection and various rheumatologic conditions and malignancies may elicit nonspecific reactions in heterophile antibody assays.

Cross-reactivity of high-titered antibodies to CMV or other herpes viruses in the EBV VCA IgM assay creates a potential source of misinterpretation that requires consideration when the differential diagnosis includes, for example, CMV or HSV infection.

HSV

Detection of circulating HSV frequently correlates with severe clinical manifestations, occurring in neonates and immunocompromised patients, as well as immunocompetent hosts. However, the incidence of subclinical HSV viremia in these populations has not been determined with certainty. HSV may be detected by NAAT in the peripheral blood of up to 25% of immunocompetent individuals experiencing primary genital HSV infection.

HSV-specific antibody titers do not predictably increase during viral reactivation from latency.

HIV

The pathogenesis of HIV cardiomyopathy/myocarditis is complex and likely multifactorial. In addition to HIV, viruses implicated in infectious myocardial disease include coxsackieviruses, CMV, and EBV.

Other HIV-associated opportunistic infections that may involve the myocardium include Toxoplasma gondii, mycobacteria, and fungi.

HCV

Cardiomyopathy due to HCV infection occurs predominantly in Asian countries, including Japan, and rarely in Western Europe and the United States. The geographic distribution of HCV-associated myocardial disease is consistent with global variations in HCV prevalence.

Seroconversion to HCV may be slow, requiring approximately 2 months on average. However, viremia may be detectable 1-3 weeks following infection. Seronegative individuals with suspected acute infection should receive NAAT for circulating HCV. Seronegative/RNA-negative individuals should be retested in 4-6 weeks and, if necessary, 4-6 months.

HCV viremia may be low-level or intermittent, and infection is not excluded by a single negative NAAT result. A negative test should be confirmed in 6-12 months.

RIBA should be reserved to confirm a positive HCV ELISA in low-risk individuals and to resolve discordances between ELISA and NAAT results.

Influenza

Although reasonably specific, rapid antigen tests for influenza lack sufficient sensitivity to exclude infection. Negative results in the setting of suspected infection should be confirmed using a more sensitive assay (e.g., culture or NAAT). Positive results from influenza rapid-antigen testing should also be confirmed by another assay during periods of low viral prevalence.

What Lab Results Are Absolutely Confirmatory?

Confirmatory Diagnostic Tests

The gold standard of antemortem myocarditis due to viral infection hinges on demonstration of concomitant inflammation, myocyte destruction, and infectious virus in EMB tissue specimens. The foundation of confirmatory testing is a set of histopathologic standards governing the microscopic assessment of disease stage and severity (Dallas criteria) supplemented by immunohistochemical surveys to differentiate and quantify infiltrating inflammatory cell populations. Preprocedure consultation with the attending pathologist to plan histologic studies guided by specimen quantity, suspected etiologies, other laboratory findings, and clinical impression is crucial.

The sensitivity of NAAT is superior to culture for virus detection in EMB specimens. Because of characteristic focality of viral myocarditic lesions, multiple biopsy specimens (typically 5-10 tissue pieces 1-2 mm3 each in size sampled from multiple areas of the right ventricular septum) are necessary to achieve satisfactory diagnostic sensitivity. Equal numbers of EMB specimens should be processed for histology and viral NAAT. Pooling of tissue pieces prior to nucleic acid extraction favors increased sensitivity of NAAT due to small sample volumes and heterogeneous viral distribution. Tissue reserved for NAAT should be submitted fresh, flash frozen, or placed in nucleic acid-stabilizing solution immediately following collection and not introduced into fixative (e.g., formalin used for histologic studies).

NAAT possesses neither perfect sensitivity nor specificity for the diagnosis of viral myocarditis, and a negative virus-specific NAAT result does not exclude the presence of infectious virions or viral nucleic acid. As NAAT does not differentiate replicating from nonreplicating virus, the significance of viral genome detection in a cardiac biopsy specimen by PCR or other NAAT method must be evaluated within the context of companion laboratory and clinical findings. Immunohistochemical examination of biopsy tissue for late life-cycle or lytic-phase viral proteins (or characteristic cytopathic effect) within myocarditic foci may aid in the discrimination of acute (active) from persistent (inactive) infection.

In situ hybridization (ISH) assays using DNA or RNA probes to detect viral nucleic acid sequences in fixed and embedded myocardial tissue sections represent an alternative to NAAT. Although less sensitive and more labor-intensive than NAAT, ISH permits direct localization of virus in tissue sections and, thereby, spatial correlation with histopathologic changes of myocarditis. However, an ISH signal would be expected for both latent and replicating virus. Probes complementary to the latency-associated transcripts, EBV-encoded RNA 1 (EBER1) and 2 (EBER2) have been used extensively for tissue diagnosis of EBV.

Definitive laboratory evidence of viral pericarditis can be obtained by demonstration of virus in pericardial fluid or tissue. The rare success of virus isolation from pericardial fluid supports use of NAAT, and possibly ISH, as the most dependable mode of virus detection. Additionally, limited data suggest that simultaneous testing of pericardial tissue improves the sensitivity of pericardiocentesis. Pathophysiologic, temporal, and etiologic overlap of viral myocarditis and pericarditis implies diagnostic commutability between these two syndromes. Therefore, a conclusively identified viral cause of myocarditis by EMB establishes the presumed etiology of pericarditis; conversely, virus detection in pericardial fluid or tissue etiologically defines an accompanying myocarditis.

Some known or suspected causes of viral myocarditis, including adenoviruses, coxsackie B, CMV, HSV, and influenza, are amenable to isolation in cell culture. Routine culturing for the agents in the premortem diagnosis of myocarditis lacks sensitivity because of insufficient specimen quantities. However, specimen availability is not a limiting factor at autopsy, and comprehensive viral culture of postmortem cardiac tissue is justified by the strong etiologic evidence established by virus isolation from the anatomic focus of disease.

Success rates of invasive diagnostic testing for suspected viral myopericarditis are inconsistent because of numerous biologic and technical variables, and the balance of risks and potential benefits associated with these procedures must be assessed for each patient. Recommendations for the use of EMB in the diagnostic evaluation of cardiomyopathy have been issued jointly by the American College of Cardiology Foundation, American Heart Association, and European Society of Cardiology.